Insulators with envelopes



JEAN lyoussou ATTOR/VE Y March 12, 1963 J. Moussou INSULATORS WITH ENVELOPES Filed Feb. 15, 1961 CEMENT CEMENT l v I I... l ulll CEMENT CEMENT United States Patent 3,081,375 INSULATORS WITH ENVELOPES Jean Moussou, Ponzac Hautes-Pyrenees, France, assrgnor to Compagnie Generale dElectro-Ceramiqne, Paris, France, a company of France Filed Feb. 15, 1961, Ser. No. 89,442 Claims priority, application France Feb. 24, 1960 6 Claims. (Cl. 174-179) The present invention relates to an improvement in insulators provided with an envelope, be they pin-type insulators or suspension insulators, designed to improve internal insulation.

As is well known, the use of hollow insulators presents the drawback that the quality of the internal insulation is liable to deteriorate due to the condensation of humidity. This drawback has been alleviated by the use of internal diaphragms for partitioning the insulator, or by employing an inert gas under pressure as a filler medium. However, such forms of execution entail extremely costly complications from the ceramics standpoint.

It is the object of this invention to provide a simple and economical envelope-type insulator, the internal insulation of which is at all times superior to the external insulation. To this end, this envelope-type insulator is provided with internal fins, the number and shape of which are such that the flashover voltage in damp atmosphere across the internal leakage path shall be greater than that under dry conditions across the leakage path of the outer profile of the envelope, thereby ensuring that arcing invariably takes place over the exterior of the insulator.

The accompanying drawing illustrates, by way of example, an envelope-type insulator, as applied to the case of a suspension insulator with central core.

In this embodiment, the insulator consists of a mechanically and electrically resistant core 1 made, for example, of bonded glass fiber, two caps 2 sealed to the core 1 by means of cement 3 and an envelope 4. In accordance with the invention, the envelope 4 is provided internally with fins 5 the number and profile of which are such that the flashover voltage in damp atmosphere across the internal leakage path is greater than that under dry conditions across the envelopes external leakage path. In a preferred embodiment, the inner fins are formed by one or more spirals, thereby enabling the profile to be produced without difliculty on a lathe by a continuous machining process.

In the embodiment in accordance with the invention, it is necessary to prevent the voltage at which arcing takes place across the leakage path on the central core from being less than that at which arcing occurs across the leakage path along the inner wall of the envelope. To this end, the insulating core may itself be provided with fins whereby the voltage at which arcing occurs across its leakage path in damp atmosphere is caused to be higher than that at which arcing takes place across the external leakage path of the envelope under dry conditions. However, as shown in the drawing, recourse may also be had to filling the annular space between the core and the envelope with an insulating substance 6 capable of closely adhering to the core. This insulating substance may be fluid, say a silicone Vaseline, or solid, such as a charged or non-charged resin; alternatively, the insulating substance may be mineral, charged or noncharged sulphur being an example.

In an insulator in accordance with the invention, namely one wherein the voltage at which arcing across the envelopes internal leakage path in damp atmosphere is greater than that at which arcing across the external leakage path occurs under dry conditions, it is permis- 3,081,375 Patented Mar. 12, 1963 sible for the internal insulating medium not to adhere closely and fully at all points along the envelope, since even in a damp ambient atmosphere the leakage path in that area is adequate to oppose arcing.

Thus the insulating substance 6 will need to satisfy only the requirement of adhering to the core 1 and not to both the core 1 and the envelope 4. Indeed, since the core 1 and the envelope 4 are generally formed from different materials having different coefiicients of expansion, this latter requirement is difficult to satisfy. In most cases, the filler medium 6 and the core 1 have coeflicients of expansion which are respectively close to and greater than that of the envelope. For this reason it is comparatively easy to bond the filler medium closely to the central core. When the filler medium is introduced in the melted state, or in the fluid state prior to polymerization, then during the contraction that occurs as the melting or polymerization temperature drops to ambient temperature, the filler substance adheres strongly to the projections 5 and separates from the portions 7. The resulting interstices in no way constitute a drawback, for even in the highly unlikely event of their communicating with one another their developed length would be greater than the envelopes internal leakage path.

With a view to improving resistance to arcing and reducing radio interference, the insulator shown in the drawing is formed in such a way that the caps 2 sealed onto the core 1 penetrate into the envelope 4 and are secured to it by means of a suitable adhesive.

If the envelope is made of a material whose coefi'icient of expansion is close to that of the filler substance adhering to the envelope, then the insulator can be constructed in such a way as to impart to the core a leakage path such that the voltage at which arcing across it takes place in damp atmosphere is greater than that at which arcing occurs across the envelopes external leakage path under dry conditions, and, when this is so, the insulator may be formed with care being taken only that the filler material adheres fully to the envelope.

Clearly, the embodiment illustrated in the drawing is by no means limiting in any sense, and any insulator, regardless of its nature or its shape, wherein the voltage at which arcing occurs across an internal leakage path in damp atmosphere is greater than the voltage at which arcing occurs across the envelopes external leakage path under dry conditions, falls within the scope of the invention.

What is claimed is:

1. An insulator of the type comprising a mechanically and electrically resistant elongated core, a cap fastened to each end of the core, and a hollow insulating envelope enclosing the coreand defining an annular space between the core and the envelope, said envelope having an internal surface and an external surface, said external surface providing an external leakage path having a predetermined flashover voltage under dry conditions, and said internal surface having formations thereon providing an internal leakage path sufliciently longer than said ex ternal leakage path that said internal surface has a flashover voltage in damp atmosphere greater than said predetermined flashover voltage.

2. An insulator as defined in claim 1, wherein said envelope has at least one spiral fin formed on the internal surface thereof, said fin providing said leakage path sufiiciently longer than said external leakage path that said internal surface has said flashover voltage indamp atmosphere greater than said predetermined flashover voltage.

3. An insulator as defined in claim 2 further comprising a layer of insulating substance disposed in said annular space and adhering closely to the core and to the furthertcomprises an external profile providing a leakage -path sufii'ciently longer thanisaid external leakage path .Iofjthe envelope that said core has a flash'over voltage in damp atmosphere greater than said predetermined flashy over voltage.

5. An insulator as defined in claim 4, wherein said core 10 has at least one spiral fin formed on the surface thereof providing vsaid leakage path'sufiicientl-y longer than said external leakage path of the envelop'ethat said core has a flasho-ver voltage in damp atmosphere greater than said ing a layer of insulating substance disposed in said annular space and adhering closely to the internal surface of the envelope and to theexternal projections of said fin formed on the surface of the core, but being separated from the portions of the core other than the fins.

References Cited in the file of this patent UNITED STATES PATENTS Steinberger '.Apr. 17, 1923 FOREIGN PATENTS 103,850 Austria July 26, 19 26 363,478 Germany Nov. 9, 1922 467,799 Germany Oct. 31, 1928 1,121,187

France Apr. 30, 1956 

1. AN INSULATOR OF THE TYPE COMPRISING A MECHANICALLY AND ELECTRICALLY RESISTANT ELONGATED CORE, A CAP FASTENED TO EACH END OF THE CORE, AND A HOLLOW INSULATING ENVELOPE ENCLOSING THE CORE AND DEFINING AN ANNULAR SPACE BETWEEN THE CORE AND THE ENVELOPE, SAID ENVELOPE HAVING AN INTERNAL SURFACE AND AN EXTERNAL SURFACE, SAID EXTERNAL SURFACE PROVIDING AN EXTERNAL LEAKAGE PATH HAVING A PREDETERMINED FLASHOVER VOLTAGE UNDER DRY CONDITIONS, AND SAID INTERNAL SURFACE HAVING FORMATIONS THEREON PROVIDING AN INTERNAL LEAKAGE PATH SUFFICIENTLY LONGER THAN SAID EXTERNAL LEAKAGE PATH THAT SAID INTERNAL SURFACE HAS A FLASHOVER VOLTAGE IN DAMP ATMOSPHERE GREATER THAN SAID PREDETERMINED FLASHOVER VOLTAGE. 